Xylose,Inulin,and Creatinine Clearance in the Normal Frog

Abstract

Hendrix, Westfall, and Richards 1 have shown from microanalyses of glomerular urine obtained directly from the exposed kidney of the frog, after intravenous injection of inulin, that it contained the same concentration of inulin as the plasma. Also, Richards and his coworkers 2 demonstrated in a double perfusion experiment that the frog's kidney was unable to excrete inulin when the fluid flowing through the intertubular capillaries contained inulin and that of the glomerular capillaries did not. Creatinine was found by them to undergo insufficient concentration in the frog renal tubules to suggest secretion.

The following experiments on normal unanesthetized bullfrogs (Rana catesbiana) were designed to determine the relation of xylose to inulin clearance, the relationship between plasma concentration of inulin and the amount excreted per unit time, and the relationship between creatinine and inulin clearances. A total of 16 normal bullfrogs, varying in weight from 280 to 600 gm. were used. Between and during collections they were kept individually in large battery jars almost completely immersed in tap water. Exogenous creatinine, inulin, xylose, and water were injected into the dorsal lymph sac. Urine was collected by catheter at half-hour or hour intervals and blood was withdrawn directly from the heart before and after each experiment.

In 9 individuals xylose was found to have a lower clearance than inulin, the average xylose to inulin ratio being 0.80. In 27 individual collection periods on 7 animals with the plasma level of exogenous creatinine varying from 11.7 to 260 mg. %, and with the urine flow ranging from 3.1 to 27.8 Ice. per kg. per hour the creatinine clearance remained practically identical with that of inulin. The average creatinine/inulin clearance ratio of all collections was 0.996, with a standard deviation of 0.0643.